Oligonucleotides of 5'-iodo-2'-deoxy-uridine are synthesized by the triester method, i.e., all the intermediates plus starting nucleotide functional groups, such as 5', 3' hydroxyl groups and phosphate groups, were protected. The 5' hydroxyl was protected with trityl groups and 3' hydroxyl by benzoyl groups. The phosphate was protected with rho-Cl-phenol and beta-cyanoethanol. Removal of protecting group was achieved by the treatment of 2% benzene sulfonyl tetrazole followed with the treatment of concentrated ammonia at 50 degrees C. The effectiveness of oligo nucleotides thus synthesized is being tested against herpes simplex virus.